Key Technologies For Dynamic Spectrum Manipulations Of Microwave Photonic Signal

Microwave photonics(MWP),which is distinguished by distributing,processing and controlling microwave signals via photonic means has received extensive attention and been widely studied in recent years for its inherent advantages brought by the photonics technologies,such as high bandwidth,high speed,low loss,immunity to electromagnetic interference,flat frequency response and parallel processing capability to process and transmit high-frequency,large-bandwidth microwave signals.Microwave photonic signal spectrum manipulations are concerning implementing spectrum-related signal processing functions for the output of the MWP system.Included technologies are spectrum filtering,frequency conversion,frequency-domain distortions compensating,signal generation and phase controlling,which are essential for the microwave application systems like modern communication,electronic warfare,radar and remote sensing detection.With the constant and rapid evolutions of new-generation microwave systems towards high-frequency bands,large bandwidth,multiple standards,multiple frequency bands and dynamic reconfiguration,broadband microwave photonic signal spectrum manipulation technologies feasible for the dynamic scenarios has become a challenging and hot research topic in the field of MWP.These new generation microwave systems are exemplified by the 5G/B5G/6G communication and military integrated electronic systems.Thus,orientated by the demands of dynamic scenario applications,in this dissertation,we will focus on three key technologies for dynamic spectrum manipulation of microwave photonic signals,covering spectrum filtering,frequency conversion and compensation of spectrum distortions for the output of microwave photonic system.Based on the theoretical analysis and experimental investigations,the main research contents of this dissertation are as following:the approaches of implementing reconfigurable microwave photonic filter(MPF)is firstly studied from the aspects of performance parameters optimization and filtering functions scalability for tunable microwave photonic filter(MPF).Then,this dissertation strives to mitigate the issues exist in classic cascaded modulators-based microwave photonic mixing architecture including poor conversion efficiency for frequency conversion and in-band interferences from image signals.Additionally,regarding the dynamic compensations of the spectrum distortions of broadband microwave signals,the typical multiband MWP system:broadband subcarrier multiplexing(SCM)radio-over-fiber system(Ro F)is considered.The microwave photonic signal spectrum distortions remain to be addressed are represented by the fiber dispersion-induced power fading and 3rd-order intermodulation distortions(IMD3).Eventually,aiming at the reconfigurable microwave photonic front-end system demanding high performance,the applications of above investigated dynamic microwave photonic signal spectrum manipulation technologies in such a system are explored.For the research of dynamic reconfigurable microwave photonic spectrum filtering,the performance parameters optimization is firstly considered.Based on the principle of polarization-modulation to intensity-modulation conversion and the two-stage stimulated Brillouin scattering(SBS)structure,an tunable MPF with ultra-high out-of-band rejection ratio is achieved.Another fast tunable single-bandpass MPF with multiple arbitrary switching flat-top passbands is enabled by the combination of a multiple phase-shifted fiber Bragg grating and the high-speed electronically controlled optical wavelength switch.As for the scalability of the filtering functions,using the classic MPF structure involving spectrum-sliced broadband optical source(BOS)and dispersive medium,a dual-band MPF for the application of duplexer with independently tunable central frequencies is implemented.Its dual-band filtering characteristics is enabled by spectrally slicing the BOS in multiple times.Also,a tunable reconfigurable MPF possessing simultaneous bandpass and bandstop filtering functions is realized through controlling the amplitudes and phases of the RF modulation sidebands along two orthogonal states of polarization.To optimize the performances of broadband cascaded modulators-based microwave photonic mixing(MPM)systems,the polarization modulation technique is applied.Through the suppression of optical carrier and photonic generations of orthogonal I/Q intermediate frequency signals,the conversion efficiency and in-band image interferences of MPMs are greatly improved and mitigated.To dynamically compensate the signal spectrum distortions for the SCM Ro F system,the bandwidth efficient optical independent-sideband modulation technique is employed to mitigate the dispersion-induced power fading and a non-iterative blind digital linearization algorithm is proposed to self-adaptively compensate the IMD3.Finally,a reconfigurable microwave photonic front-end featuring broadband and high dynamic range is constructed based on a spectrum-sliced BOS,a DDMZM,dispersive medium and digital post processing.The main research results and major contributions of this dissertation are as listed in the following:First,an tunable MPF with ultra-high out-of-band rejection ratio is realized.Verified by the experiments,this MPF can achieve an ultrahigh processing resolution(<7.7 MHz)and a out-of-band rejection ratio as high as 80 d B.Furthermore,by controlling the frequency of the pump lightwave,continuous tuning of the central frequency from 2.1 GHz to 6.1 GHz while maintaining excellent out-of-band rejection ratio performance is demonstrated.On the other hand,a fast tunable single-bandpass MPF with multiple arbitrary switching flat-top passbands is experimentally demonstrated.In experiments,the shape factor of the measured filtering response is 2.27 and the tuning speed is as fast as 1.73 ns.In addition,up to 41 d B out-of-band ratio and capability of multiple arbitrary switching passbands within its entire12-GHz operation range are experimentally observed.(Chapter 3)Second,a dual-band MPF for the application of duplexer with independently tunable central frequencies is implemented.Its dual-band filtering characteristics is enabled by using a differential-group-delay interferometer(DGDI)and a Mach–Zehnder interferometer(MZI)to spectrally slice the BOS in multiple times.In experiments,tunable ranges from 0 to 6.1GHz and from 0 to 17 GHz for two independent filtering channels are achieved.Meanwhile,a high isolation up to 44 d B between them is also obtained.A tunable MPF can simultaneously provide the functions of channel selection,interference rejection and complementary filtering outputs is implemented by using an integrated polarization division-multiplexing MZM and the in-fiber SBS effect.Two complementary responses are simultaneously generated in a high frequency resolution of?20 MHz,with a rejection over35 or 51 d B being achieved for the passband or stopband.A tunable central frequency to the bandpass and bandstop responses is also demonstrated within the range from 3 to 15 GHz.(Chapter 3)Third,two cascaded polarization modulators(Pol Ms)are used for the effective optical carrier suppression without the need of any optical filtering.With this structure,the limitation of lower operation frequency can be eliminated and a microwave photonic mixer with high conversion efficiency within a full frequency range coverage is obtained.The conversion efficiency is improved by over 20 d B within the radiofrequency(RF)range from2 to 15 GHz,compared to the classic structure of cascaded Mach-Zehnder modulators(MZMs).Inspired from the Hartley image-reject architecture,cascaded phase modulator and Po IM are employed to construct an image-free microwave mixer.The Pol M is incorporated with single-sideband modulation and polarizers to generate two orthogonal in-phase(I)and quadrature(Q)intermediate frequency(IF)signals.Assisted by the real-time analog electrical and offline digital post processing,image rejection ratios over 45 and 60 d B are achieved separately.(Chapter 4)Fourth,with the aid of the collaboration of bandwidth efficient optical independent-sideband modulation technique and newly proposed guard band-free SCM channel frequency allocation scheme,the transmission of broadband signal(>22.5 GHz)over the long-distance fiber link(>50 km)is successfully demonstrated.While the required electrical bandwidth is less than 15 GHz.indicating an improvement factor of 1.5 for bandwidth efficiency of the proposed system.A digital non-iterative blind linearization algorithm is proposed to compensate the IMD3 signal in a self-adaptive manner and the flexible compensation of the dispersion-induced power fading is facilitated through controlling the modulation chirp of the single-driven DDMZM.By combining the power fading compensation and the IMD3 suppression,the transmissions of 64-QAM-OFDM SCM signals in 1 to 12 SCM channels with a 500-MHz bandwidth has been experimentally demonstrated over standard single-mode fibers(SSMFs)set at various lengths,20,50 and100 km.(Chapter 5)Fifth,a high-performance and reconfigurable microwave photonic front-end capable of performing spectrum-distortions compensation is implemented.Demonstrated by the experiments,this microwave photonic front-end system is capable of performing photonic-assisted reconfigurable RF signal bandpass filtering,broadband mixing and IF bandpass filtering,while with dispersion and nonlinearity penalties compensations.Finally,the power losses of the filtering channels or IF signals affected by the dispersion-induced power fading is compensated through the bias controlling of the DDMZM,facilitating continuous tunings of the central frequencies of the filtering and intermediate frequency(IF)responses ranging from 0 to 15 GHz is observed.On the other hand,the IMD3 is effectively suppressed through the digital post-processing using proposed non-iterative blind linearization algorithm,resulting in great improvements of spurious dynamic ranges(SFDR)from 87.6 d B·Hz^2/3 to 112 d B·Hz^4/5for the filtering mode and 81 d B·Hz^2/3 to 103.7 d B·Hz^4/5for the mixing mode.(Chapter 6)In summary,this dissertation concentrates on the spectrum manipulation of microwave photonic signals in dynamic scenarios and three key technologies including spectrum filtering,frequency conversion and compensation of spectrum distortions are studied.For the microwave photonic spectrum filtering,a plurality of MPF schemes are proposed to achieve filtering performances enhancement and functions expansion.For the microwave photonic frequency conversion,two MPM structures are designed to effectively improve and mitigate the conversion efficiency and in-band image interferences for the cascaded modulators-based MPM systems.For the compensations of spectrum distortions,the optical independent sideband modulation technique is introduced to alleviate the problem of dispersion-induced power fading and concurrently improve the spectral efficiency of the SCM Ro F system.Also,a non-iterative blind linearization algorithm is proposed to satisfy the requirement of self-adaptively compensate IMD3 in dynamic scenarios with features of system capacity saving and low processing delay.The applications of above investigated technologies to the microwave photonic front-end system is finally explored,resulting in a reconfigurable microwave photonic front-end featuring broad bandwidth and high dynamic range.